全文获取类型
收费全文 | 2510篇 |
免费 | 126篇 |
国内免费 | 9篇 |
专业分类
2645篇 |
出版年
2024年 | 4篇 |
2023年 | 30篇 |
2022年 | 65篇 |
2021年 | 126篇 |
2020年 | 75篇 |
2019年 | 64篇 |
2018年 | 109篇 |
2017年 | 88篇 |
2016年 | 109篇 |
2015年 | 162篇 |
2014年 | 187篇 |
2013年 | 220篇 |
2012年 | 207篇 |
2011年 | 185篇 |
2010年 | 113篇 |
2009年 | 110篇 |
2008年 | 123篇 |
2007年 | 115篇 |
2006年 | 111篇 |
2005年 | 75篇 |
2004年 | 57篇 |
2003年 | 51篇 |
2002年 | 37篇 |
2001年 | 11篇 |
2000年 | 11篇 |
1999年 | 12篇 |
1998年 | 16篇 |
1997年 | 16篇 |
1996年 | 12篇 |
1995年 | 7篇 |
1994年 | 8篇 |
1993年 | 15篇 |
1991年 | 5篇 |
1990年 | 5篇 |
1989年 | 7篇 |
1988年 | 4篇 |
1987年 | 8篇 |
1986年 | 3篇 |
1985年 | 7篇 |
1984年 | 7篇 |
1983年 | 4篇 |
1981年 | 5篇 |
1980年 | 7篇 |
1979年 | 3篇 |
1978年 | 6篇 |
1977年 | 8篇 |
1976年 | 4篇 |
1972年 | 4篇 |
1971年 | 7篇 |
1969年 | 3篇 |
排序方式: 共有2645条查询结果,搜索用时 0 毫秒
71.
72.
Mohammad Firdaus Bin Abdul Aziz Michael Morrison Jane Kaye 《New genetics and society》2018,37(1):2-20
Many “rising powers” such as India, China, Argentina, Singapore, and Brazil are investing in stem cell technology, joining the traditional leaders in the field, such as the UK, Germany, USA, and Japan. Malaysia is also entering this sector because of the potential medical and economic benefits that the use of stem cell technologies could provide. Like other countries, Malaysia faces the challenge of how to encourage scientific progress and innovation in an ethical manner while at the same time ensuring a safe and accessible market for regenerative therapies. This paper reports on the research findings of semi-structured interviews with local stakeholders to investigate how they perceived and evaluated the current regulatory framework for human stem cell research in Malaysia, and what might be at stake if the state continues with its current regulatory approach. 相似文献
73.
The paleobiogeography of hominoids exhibits a puzzling pattern of migrations between and within Africa and Eurasia. A precise dating of hominoid-bearing localities is therefore essential to reveal the timing, direction and possible causes of dispersals. Here, we present a bio-magnetostratigraphic analysis of the section of Engelswies (Southern Germany, Upper Freshwater Molasse, North Alpine Foreland Basin) where the oldest Eurasian hominoid was found. Our paleomagnetic results reveal a very short normal and a reverse magnetic polarity for the entire section. The polarity record is correlated to the Astronomical Tuned Neogene Time Scale using an integrated stratigraphic approach. This approach follows the chronostratigraphic framework for the Upper Freshwater Molasse, which combines magnetostratigraphy with biostratigraphic, lithostratigraphic and 40Ar/39Ar dating results. According to this outcome, the reverse polarity of the Engelswies section most likely correlates to magnetochron C5Cr. The origin of the short normal polarity remains enigmatic. The magnetostratigraphic calibration and the evolutionary level of the Engelswies small mammal fauna suggest an age of 17.1-17.0 Ma (Early Karpatian, Early Miocene) for the oldest Eurasian hominoid, and roughly confirm the estimates of Heizmann and Begun (2001). The estimated age suggests that the first hominoids in Eurasia are contemporaneous with Afro-Arabian afropithecins, and dispersal may have been facilitated by intra-Burdigalian (∼18-17 Ma) sea-level low stands and the beginning of the Miocene Climate Optimum. The paleoclimatic and environmental reconstruction of the Engelswies locality indicates a lakeshore environment near dense subtropical rain forest vegetation, where paratropical temperatures (mean annual temperature around 20 °C) and humid conditions (mean annual precipitation > 1.100 mm) prevailed. 相似文献
74.
Abdul Hakeem Jerome F. Grant Gregory J. Wiggins Paris L. Lambdin James R. Rhea 《Biocontrol Science and Technology》2011,21(6):687-691
The coexistence of two introduced predatory species, Laricobius nigrinus Fender and Sasajiscymnus tsugae (Sasaji and McClure), and a native predator, L. rubidus LeConte, on eastern hemlock was documented for the first time. Details of their coexistence and implications to management of hemlock woolly adelgid, Adelges tsugae Annand, are discussed. 相似文献
75.
Ahsg (fetuin-A) is a 55-59 kDa phosphorylated glycoprotein synthesized in the adult predominantly by hepatocytes, from which it enters the circulation. When dysregulated, this glycoprotein operates to influence the clinical sequelae of insulin resistance-type 2 diabetes and cardiovascular disease. The pathological sequelae likely arise from two separable molecular “faces” of Ahsg—one acting at the level of the insulin receptor and a second face influencing ectopic biomineralization in the intima. A detailed understanding of these two functional faces of Ahsg is not yet clear for lack of structural studies. Ahsg has a physiological role in the biomineralization of bone, which when dysregulated can lead to ectopic calcification of soft tissues in the vasculature. Ahsg has a second physiological function in regulating how insulin signals through its receptor, a transmembrane tyrosine kinase. Dysregulation of this “face” of Ahsg results in morbid sequelae such as impaired glucose disposal and fatty liver. Ahsg binds to tandem fibronectin type 3 (Fn3) domains present in the 194 amino acid residue extracellular portion of the β-subunit of the insulin receptor, distant from the high-affinity pocket formed by two complementing α-subunits where insulin binds. Only two proteins are known to bind directly to the insulin receptor ectodomain - insulin and Ahsg - the former turns on the receptor's intrinsic tyrosine kinase (TK) activity, and the latter shuts it down. Recent X-ray crystallographic studies of the ectodomain of the insulin receptor now sharpen our understanding of the receptor's extracellular α-subunit and linked β-subunit. Ahsg genotype and its circulating level have been correlated with body morphometrics (obese versus lean and visceral adiposity) in epidemiological studies enrolling thousands of patients. Epidemiological studies from the clinic reveal high levels of circulating Ahsg in insulin resistance and diabetes. This review endeavors to explain how one protein can mediate diverse pathologies, but specifically addresses its metabolic “face” blunting insulin receptor activity, an action leading to insulin resistance. 相似文献
76.
Baharum H Morita H Tomitsuka A Lee FC Ng KY Rahim RA Abe I Ho CL 《Marine biotechnology (New York, N.Y.)》2011,13(5):845-856
Type III polyketide synthases (PKSs) produce an array of metabolites with diverse functions. In this study, we have cloned
the complete reading frame encoding type III PKS (SbPKS) from a brown seaweed, Sargassum binderi, and characterized the activity of its recombinant protein biochemically. The deduced amino acid sequence of SbPKS is 414
residues in length, sharing a higher sequence similarity with bacterial PKSs (38% identity) than with plant PKSs. The Cys-His-Asn
catalytic triad of PKS is conserved in SbPKS with differences in some of the residues lining the active and CoA binding sites.
The wild-type SbPKS displayed broad starter substrate specificity to aliphatic long-chain acyl-CoAs (C6–C14) to produce tri- and tetraketide pyrones. Mutations at H331 and N364 caused complete loss of its activity, thus suggesting that these two residues are the catalytic residues for SbPKS as in
other type III PKSs. Furthermore, H227G, H227G/L366V substitutions resulted in increased tetraketide-forming activity, while
wild-type SbPKS produces triketide α-pyrone as a major product. On the other hand, mutant H227G/L366V/F93A/V95A demonstrated
a dramatic decrease of tetraketide pyrone formation. These observations suggest that His227 and Leu366 play an important role for the polyketide elongation reaction in SbPKS. The conformational changes in protein structure especially
the cavity of the active site may have more significant effect to the activity of SbPKS compared with changes in individual
residues. 相似文献
77.
78.
Abdul Latif Khan Muhammad Hamayun Yoon-Ha Kim Sang-Mo Kang In-Jung Lee 《Plant Physiology and Biochemistry》2011,49(8):852-861
Experiments were conducted to investigate the role of a newly isolated endophytic fungus GMC-2A on physiology of host plant (Glycine max. L cv. Hwangkeum-kong) growing under salinity stress. GMC-2A was identified as a new strain of Penicillium funiculosum on the basis of sequence homology and phylogenetic analysis of D1/D2 regions of 28S rDNA. Preliminary screening experiment showed that the culture filtrate (CF) of GMC-2A promoted the growth of Waito-C, a dwarf gibberellin (GA) biosynthesis mutant rice cultivar. Analysis of fungal CF revealed the presence of GAs (GA1 1.53 ng/ml; GA4 9.34 ng/ml; GA8 1.21 ng/ml; GA9 37.87 ng/ml) and indole acetic acid (14.85 μg/ml). GMC-2A also showed high phosphate solubilization of tricalcium phosphate. Besides that, GMC-2A application enhanced soybean seed germination as compared to control. Under salinity stress (70 and 140 mM), GMC-2A significantly promoted the soybean growth attributes (shoot length, shoot fresh/dry biomass, chlorophyll content, photosynthesis rate and leaf area) in comparison to control treatments. We also observed low endogenous abscisic acid and elevated jasmonic acid contents in GMC-2A treated plants under salt stress. GMC-2A treatment significantly enhanced levels of isoflavones (34.22% and 75.37%) under salinity stress as compared to control. In conclusion, P. funiculosum LHL06 has significantly ameliorated the adverse effects of salinity induced abiotic stress, and re-programmed soybean to higher growth and isoflavone biosynthesis. 相似文献
79.
Jeyasekaran G. Raj K. Thirumalai Shakila R. Jeya Thangarani A. Jemila Sukumar D. Jailani V. Abdul Kadhar 《World journal of microbiology & biotechnology》2011,27(4):953-959
A multiplex PCR based assay was developed for the identification of the genus Salmonella. Five sets of primers from different genomic sequences such as fimA, himA,
hns, invA and hto genes were selected for the identification of serogroups of Salmonella
enterica such as S. Typhi, S. ParatyphiA, S. Typhimurium, S. Enteritidis and S. Weltevreden. The selected primers amplified products with the sizes of 85, 123, 152, 275 and 496 bp, respectively, for the
genus Salmonella. This assay was found to be highly sensitive, as it could detect 5 cells of Salmonella and 1,000 fg of genomic DNA. Amplification of DNA extracted from other genera viz. V. cholerae and E. coli yielded negative results. This assay provides specific and reliable results and allows for the cost–effective detection of
Salmonella in one reaction tube in mixed bacterial communities. 相似文献
80.
Abdul Hamid 《Plant and Soil》1972,36(1-3):709-711